A printer is known, in which a continuous form such as a fan folded form or the like can be fed bi-directionally by a pair of tractors of a bi-directional form feeder unit. In the known printer, a portion of the continuous form extending between a platen and the tractors tends to slacken due to various factors, including variation in thickness of the continuous form, variation in pitch of sprocket holes formed along opposite side edges of the continuous form, a change in humidity of the environment, and so on.
Various measures have conventionally been taken to prevent the above-mentioned slackening. Japanese Utility Model Application Laid-Open No. 58-99061 discloses an arrangement in which a tension roller is arranged between the platen and the tractors to apply tension to the continuous form, thereby taking up the slack. Further, Japanese Utility Model Publication No. 57-42676 discloses an arrangement in which a pair of support plates are mounted respectively to opposite axial ends of a guide shaft of the form feeder unit, and are moved angularly about the axis of the guide shaft by means of a cam mechanism, to adjust tension acting upon the continuous form. In the former arrangement, the tension roller is not uniformly abutted against the continuous form due to distortion thereof, but is abutted against the continuous form in a one-sided manner, or an amount of deflection of the continuous form varies depending upon the types or kinds of the continuous form. This results in variation in the printing quality. On the other hand, it is required for the latter arrangement to arrange cams and associated mechanisms independently of the tractors, that is, on the outside of the form feeder unit. This results in complication in arrangement of various components around the form feeder unit, making maintenance and inspection troublesome and difficult.